Extruded Titania-Based Materials Comprising One or More Acids or Prepared Using One or More Acids

ABSTRACT

Porous, extruded titania-based materials further comprising one or more acids and/or prepared using one or more acids, Fischer-tropsch catalysts comprising them, uses of the foregoing, processes for making and using the same and products obtained from such processes.

The present invention relates to a porous, extruded titania-basedmaterial further comprising one or more acids and/or prepared using oneor more acids, particularly a porous, extruded titania-based materialhaving improved crush strength and being suitable for use as a catalystsupport more particularly a Fischer-Tropsch catalyst support. Theinvention also relates to a porous, extruded titania-based materialfurther comprising one or more acids and/or prepared using one or moreacids, and comprising mesopores and macropores. The invention furtherrelates to processes for the preparation of a porous, extrudedtitania-based material further comprising one or more acids and/orprepared using one or more acids, and processes for the production ofFischer-Tropsch synthesis catalysts comprising such material.

The conversion of synthesis gas into hydrocarbons by the Fischer-Tropschprocess has been known for many years. The growing importance ofalternative energy sources has seen renewed interest in theFischer-Tropsch process as one of the more attractive direct andenvironmentally acceptable routes to high quality transportation fuels.

Many metals, for example cobalt, nickel, iron, molybdenum, tungsten,thorium, ruthenium, rhenium and platinum are known to be catalyticallyactive, either alone or in combination, in the conversion of synthesisgas into hydrocarbons and oxygenated derivatives thereof. Of theaforesaid metals, cobalt, nickel and iron have been studied mostextensively. Generally, the metals are used in combination with asupport material, of which the most common are alumina, silica andcarbon.

In the preparation of metal-containing Fischer-Tropsch catalyst, a solidsupport is typically impregnated with a metal-containing compound, suchas a cobalt-containing compound, which may for instance be anorganometallic or inorganic compound (e.g. Co(N₃)₂.6H₂O), by contactingwith a solution of the compound. The particular form of metal-containingcompound is generally selected for its ability to form an appropriateoxide (for example CO₃O₄) following a subsequent calcination/oxidationstep. Following generation of the supported metal oxide, a reductionstep is necessary in order to form the pine metal as the activecatalytic species. Thus, the reduction step is also commonly referred toas an activation step.

It is known to he beneficial to perform Fischer-Tropsch catalysis withan extrudate, particularly in the case of fixed catalyst bed reactorsystems. It is, for instance, known that for a given shape of catalystparticles, a reduction in the size of the catalyst particles in a fixedbed gives rise to a corresponding increase in pressure drop through thebed. Thus, the relatively large extrudate particles cause less of apressure drop through the catalyst bed in the reactor compared to thecorresponding powdered or granulated supported catalyst. It has alsobeen found that extrudate particles generally have greater strength andexperience less attrition, which is a particular value in fixed bedarrangements where bulk crush strength may be very high.

An impregnated extrudate may be formed by mixing a solution of ametal-compound with a support material particulate, mulling, andextruding to form an extrudate before drying and calcining.Alternatively, an extrudate of a support material is directlyimpregnated, for instance by incipient wetness, before drying andcalcining.

Commonly used support materials for Fischer-Tropsch catalysts includealumina, silica and carbon; however, a particularly useful material isextruded titania (titanium dioxide). Extruded titania support materialstypically have a mesoporous structure, i.e. the extruded materialcomprises pores having a pore size of 2 to 50 nm.

Titania is also extensively used as a catalyst in the Claus process thatconverts gaseous sulphur compositions into sulphur.

Although titania-based extrudates have been produced on a commercialscale, they generally suffer from poor mechanical (crash) strength,which makes the manufacturing, handling and loading of the catalyst intoa reactor difficult. Moreover, in a fixed reactor, extrudates aresubject to demanding conditions and have to tolerate stress from axialpressure difference, pressure oscillation in the process, surge ofliquid flow, and the weight of catalyst in the upper bed, to list a few.Fracture failure of weak extrudates could cause catastrophic pressuredrop in the process, and the particulates generated from crumbledextrudates could cause dysfunction or malfunction of downstream devicesand equipment. This problem is worsened in extrudates hawng increasedporosity, as the introduction of additional pores, particularlymacrospores, further reduces the crush strength of the extrudates.

Various inorganic binders have been investigated to reinforce thestructure of titania-based extrudates, and these include alumina andalumina-based composites, clays, boric acid, and activated titania andtitania-based composites.

WO 2007/068731 discloses a process for the preparation of a catalyst orcatalyst precursor, comprising the steps of; (a) admixing: (i) acatalytically active metal or metal compound, (ii) a carrier material,(iii) a gluing agent, and (iv) optionally one or more promoters, and/orone or more co-catalysts; (b) forming the mixture of step (a); anddrying the product of step (b) for more than 5 hours at a temperature upto 100° C. to form the catalyst or catalyst precursor. The catalyticallyactive metal may comprise cobalt, iron or ruthenium, the carriermaterial may comprise titanium, and the forming step may compriseextrusion. The gluing agent may be selected from a wide range ofmaterials, including various organic acids, such as amino acids mono-,di- or tri-carboxylic acids, derivatives thereof or poly-carboxylicacids. The process specifically excludes a calcining step.

There therefore remains a need for porous, extruded titania-basedmaterial having improved crush strength, particularly a porous, extrudedtitania-based material comprising mesopores and macrospores and havingimproved crush strength.

It has now surprisingly been found that incorporating one or more acids,particularly aqueous solutions thereof, during the extrusion of atitania-based material improves the crush strength of the porous,extruded titania-based material. Surprisingly, the incorporation of oneor more acids in the extrusion process has little impact on the porosityof the finished support, and even when macropores are introduced intothe extrudates the use of one or more acids increases the crush strengthof the macroporous supports.

Thus, in a first aspect the present invention provides a porous,extruded titania-based material thither comprising one or more acids,particularly a porous, extruded titania-based material comprisingmesopores and macropores and further comprising one or more acids,

The present invention further provides a process for the preparation ofa porous, extruded titania-based material having a crush strengthgreater than 3.0 lbf, said process comprising:

-   -   a) mixing titanium dioxide and one or more acids, and optionally        a liquid extrusion medium, to form a homogenous paste;    -   b) extruding the paste to form an extrudate; and    -   c) drying and/or calcining the extrudate.

The present invention further provides a process for the preparation ofa porous, extruded titania-based material comprising mesopores andmacropores and having a crush strength greater than 3.0 lbf, saidprocess comprising:

-   -   a) mixing titanium dioxide and one or more porogens to form a        homogenous mixture;    -   b) adding one or more, acids, and optionally a liquid extrusion        medium, to the homogenous mixture, and mixing to form a        homogenous paste;    -   c) extruding the paste to form an extrudate; and    -   d) drying and/or calcining the extrudate at a temperature        sufficient to decompose the one or more porogens.

The present invention yet further provides a porous, extrudedtitania-based material obtainable by a process according to theinvention.

The present invention further provides a Fischer-Tropsch synthesiscatalyst comprising a porous, extruded titania-based material accordingto the invention, and further comprising at least one metal selectedfrom cobalt, iron, nickel, ruthenium or rhodium, particularly aFischer-Tropsch synthesis catalyst comprising a porous, extrudedtitania-based material according to the invention comprising mesoporesand macropores, and further comprising at least one metal selected fromcobalt, iron, nickel, ruthenium or rhodium.

The present invention yet further provides a process for the preparationof a Fischer-Tropsch synthesis catalyst according to the invention, saidprocess comprising:

-   -   a) mixing titanium dioxide, one or more acids, optionally a        liquid extrusion medium, and a solution of at least one        thermally decomposable cobalt, iron, nickel, ruthenium or        rhodium compound, to form a homogenous paste;    -   b) extruding the paste to form an extrudate;    -   c) drying and/or calcining the extrudate at a temperature        sufficient to convert the one or more thermally decomposable        cobalt, iron, nickel, ruthenium or rhodium compound to an oxide        thereof; or to the metal form; and, where an oxide is formed,        optionally    -   d) heating the dried and/or calcined extrudate under reducing        conditions to convert the one or more cobalt, iron, nickel,        ruthenium or rhodium oxide to the metal form.

The present invention further provides a process for the preparation ofa Fischer-Tropsch synthesis catalyst comprising a porous, extrudedtitania-based material comprising mesopores and macropores according tothe invention, said process comprising:

-   -   a) mixing titanium dioxide and one or more porogens to form a        homogenous mixture;    -   b) adding one or more acids, optionally a liquid extrusion        medium, and a solution of at least one thermally decomposable        cobalt, iron, nickel, ruthenium or rhodium compound to the        mixture, and mixing to form a homogenous paste;    -   c) extruding the paste to form an extrudate;    -   d) drying and/or calcining the extrudate at a temperature        sufficient to decompose the one or more porogens and to convert        the at least one thermally decomposable cobalt, iron, nickel,        ruthenium or rhodium compound to an oxide thereof, or to the        metal form; and, where an oxide is formed, optionally    -   e) heating the dried and/or calcined extrudate under reducing        conditions to convert the one or more cobalt, iron, nickel,        ruthenium or rhodium oxide to the metal form.

The present invention yet further provides a process for the preparationof a Fischer-Tropsch synthesis catalyst according to the invention, saidprocess comprising:

-   -   a) impregnating a porous, extruded titania-based material        according to the invention with a solution of at least one        thermally decomposable cobalt, iron, nickel, ruthenium or        rhodium compound;    -   b) drying and/or calcining the impregnated porous, extruded        titania-based material at a temperature sufficient to convert        the at least one thermally decomposable cobalt, iron, nickel,        ruthenium or rhodium compound to an oxide thereof or to the        metal form; and where an oxide is formed, optionally    -   c) heating the dried and/or calcined porous, extruded        titania-based material under reducing conditions to convert the        at least one cobalt, iron, nickel, ruthenium or rhodium oxide to        the metal form.

There is yet further provided a Fischer-Tropsch synthesis catalystobtainable by a process according to the invention, preferably having acrush strength of greater than 5.0 lbf.

There is yet further provided the use of one or more acids to prepare aporous, extruded titania-based material, preferably comprising mesoporesand macropores, having a crush strength of greater than 3.0 lbf, andalso the use of one or more acids to prepare a porous, extrudedtitania-based Fischer-Tropsch synthesis catalyst, preferably comprisingmesopores and macropores, having a crush strength of greater than 5.0lbf.

In a further aspect, the present invention provides a process forconverting a mixture of hydrogen and carbon monoxide gases tohydrocarbons, which process comprises contacting a mixture of hydrogenand carbon monoxide with a Fischer-Tropsch synthesis catalyst accordingto the invention or a Fischer-Tropsch synthesis catalyst obtainable by aprocess according to the invention.

In a further aspect, the present invention provides a composition,preferably a fuel composition, comprising hydrocarbons obtained by aprocess according to the invention.

In a further aspect, the present invention provides a process forproducing a fuel composition, said process comprising blendinghydrocarbons obtained by a process according to the invention with oneor more fuel components to form the fuel composition.

The porous, extruded titania-based material according to the presentinvention may be prepared using any acids capable of increasing thestrength of titania-based extrudates. Without wishing to be bound bytheory, it is believed that when titania nanocrystals, particularlyanatase and/or rutile polymorphs thereof, are extruded, the particlesformed generally lack cross-linkages based on chemical bondinteractions, and that the forces that hold these particles togetherwhen they are formulated with water are mainly van der Waals forces, butthat activation of the titania particles with one or more acids maycatalyse the hydrolysis of Ti—O—Ti units, generating Ti—OH units on thesurface of the titania nanoparticles. Condensation of these hydroxylgroups at an elevated temperature may then generate chemical bondinginteractions between these crystallites, and accordingly substantiallyimprove mechanical strength of the extrudates.

Suitable acids for use in the present invention may be organic acids(carboxylic acids) or inorganic acids (also referred to as mineralacids), and include, but are not limited to, propionic acids, malicacid, oxalic acid, valeric acid, carbonic acid, formic acid, citricacid, acetic acid, nitric acid, hydrochloric acid, hydrofluoric acid,hydrobromic acid, hydroiodic acid, phosphoric acid, sulphuric acid andmixtures thereof, preferably acetic acid, formic acid, citric acid,nitric acid and mixtures thereof, more preferably nitric acid, aceticacid and mixtures thereof.

As noted above, the improvement in crush strength provided by mixing oneor more acids with titanium dioxide before extrusion remains followingextrusion, even if the one or more acids are partially or even entirelyremoved during and/or after extrusion. Thus, porous, extrudedtitania-based materials according to the present invention may furthercomprise one or more acids, or may be entirely free of such compounds.Preferably, the total amount of one or more acids is at least partiallyreduced in the porous, extruded titania-based material of the presentinvention compared to the amount present during the formation of thematerial, and more preferably the porous, extruded titania-basedmaterial is substantially or entirely free of acids.

The one or more acids used in the preparation of porous, extrudedtitania-based materials according to the present invention may beremoved therefrom in any suitable mariner, such as by thermodecomposition or oxidation, for example by heating the extrudates to430° C. or higher, preferably 500° C. or higher, in air.

The total amount of one or more acids used in the preparation of porous,extruded titania-based materials according to the present invention maybe any amount sufficient to provide improvements in the crush strengthof the finished extrudates, but preferably no more than can berelatively easily removed from the extrudates following extrusion.Preferably the one or more acids are used at concentrations of 0.1mol/litre or above; for example, preferably 0.1 mol/litre or above, morepreferably 0.5 mol/litre or above, for nitric acid; or preferably 0.5mol/litre or above, more preferably 1.0 mol/litre or above, for aceticacid. The upper limit of the concentration of the one or more acids isnot critical, so long as it does not exceed the solubility of thespecific acid or acids being used. The crush strength of the porous,extruded titania-based material according to the present invention maybe measured by any suitable method known to those skilled in the art,for example using equipment designed to comply with ASTM D4179-01standards, such as a Varian Benchsaver™ V200 Tablet Hardness Tester.Alternatively, crush strength may be measured using equipment designedto comply with ASTM D6175-03 standards.

The porous, extruded titania-based material according to the presentinvention suitably has a crush strength of greater than 3.0 lbf,preferably greater than 5.0 lbf, more preferably greater than 8.0 lbf.The upper limit of the crush strength is not critical; however, asuitable maximum crush strength may be 20 lbf. A particularly preferredrange of crush strength for a porous, extruded titania-based materialaccording to the present invention is 3.0 lbf to 20.0 lbf, such as 5.0lbf to 15.0 lbf, 5.0 lbf to 12.0 lbf or 8.0 lbf to 12.0 lbf.

The porous, extruded titania-based material according to the presentinvention generally has a symmetrical geometry that includes, but is notlimited to, cylinders, spheres, spheroids, pastilles, dilobes, such ascylindrical dilobes, trilobes, such as cylindrical trilobes,quadralobes, such as cylindrical quadralobes, and hollow cylinders.

The pore diameter of the porous, extruded titania-based materialaccording to the present invention may be measured by any suitablemethod known to those skilled in the art, for example scanning electronmicroscopy or mercury porosimetry based on mercury intrusion using theWashburn equation with a mercury contacting angle of 130° and a mercurysurface tension of 485 dynes/cm. As used herein, the term “porediameter” equates with “pore size” and consequently refers to theaverage cross-sectional dimension of the pore, understanding, as theskilled person does, that a determination of pore size typically modelspores as having circular cross-sections.

Preferably, the porous, extruded titania-based material comprisingmesopores and macrospores according to the present invention, comprisesa multi-modal distribution of pores, i.e. the material comprises a rangeof pore sizes/pore diameters with two or more modes, such as two, three,four or more modes. Particularly suitable materials comprise a bi-modaldistribution of pore sizes/pore diameters, i.e. a range of poresizes/pore diameters comprising two modes, the first mode representingmesopores and the second mode representing macropores.

The porous, extruded titania-based material comprising mesopores andmacropores according to the present invention suitably comprisesmesopores having a pore diameter of 2 to 50 nm, for example 5 to 50 nm,preferably 15 to 45 nm or 20 to 45 nm, more preferably 25 to 40 nm or 30to 40 nm.

The porous, extruded titania-based material comprising mesopores andmacropores according to the present invention suitably comprisesmacrospores having a pore diameter of greater than 50 nm, preferably 60to 1000 nm, more preferably 100 to 850 nm.

The pore volume of a porous, extruded titania-based material comprisingmesopores and macropores according to the present invention may bemeasured by any suitable method known to those skilled in the art, forexample using mercury porosimetry.

Suitably, the porous, extruded titania-based material according to thepresent invention has a total pore volume of at least 0.30 ml/g,preferably at least 0.40 ml/g, more preferably at least 0.50 ml/g. Theupper limit of the total pore volume is not critical, so long as thematerial remains sufficiently robust to function as a catalyst support;however, a suitable maximum pore volume may be 1.00 ml/g, preferably0.90 ml/g. Particularly preferred ranges of total pore volume for aporous, extruded titania-based material comprising mesopores andmacropores further comprising zirconium oxide according to the presentinvention are 0.30 to 1.00 ml/g, such as 0.40 to 1.00 ml/g, 0.40 to 0.90ml/g or 0.50 to 0.90 ml/g.

The surface area of the porous, extruded titania-based materialcomprising mesopores and macropores according to the present inventionmay be measured in any suitable way known to those skilled in the art,such, as by nitrogen porosimetry using the BET model to the nitrogenadsorption isotherm collected at 77K on a Quadrasorb SI unit(Quantachrome).

Suitably, the porous, extruded titania-based material comprisingmesopores and macropores according to the present invention has asurface area of at least 30 m²/g, preferably at least 40 m²/g. The upperlimit of the surface area is not critical, so long as the material issuitable for the intended use, such as a catalyst support; however, asuitable maximum surface area may be 60 m²/g or 55 m²/g. A particularlysuitable range of surface area for a porous, extruded titania-basedmaterial comprising mesopores and macropores of the present invention is30 to 60 m²/g, preferably 40 to 55 m²/g.

The BET surface area, pore volume, pore size distribution and averagepore radius of a porous, extruded titania-based material comprisingmesopores and macropores may additionally be determined from thenitrogen adsorption isotherm determined at 77K using a MicromeriticsTRISTAR 3000 static volumetric adsorption analyser. A procedure whichmay be used is an application of British Standard method BS4359: Part 1:1984, “Recommendations for gas adsorption (BET) methods” and BS7591:Part 2: 1992, “Porosity and pore size distribution of materials”—Methodof evaluation by gas adsorption. The resulting data may be reduced usingthe BET method (over the pressure range 0.05-0.20 P/P₀) and the Barrett,Joyner & Halenda (BJH) method (for pore diameters of 2 to 100 nm) toyield the surface area and pore size distribution respectively. Nitrogenporosimetry, such as described above, is the preferred method fordetermining the surface areas of the extruded titania-based materialsaccording to the present invention.

Suitable references for the above data reduction methods are Brunaeur,S, Emmett, P H, and Teller, E; J. Amer. Chem. Soc. 60, 309, (1938) andBarrett, E P, Joyner, L G and Halenda, P P; J Am. Chem. Soc., 1951, 73,375 to 380.

As a further alternative, pore volume may be estimated through mercuryporosimetry by use of an AutoPore IV (Micromeritics) instrument, andpore diameter may be measured from the mercury intrusion branch usingthe Washburn equation with a mercury contacting angle at 130° and amercury surface tension of 485 dynes/cm. Further details are provided inASTM D4284-12 Standard Test Method for Determining Pore VolumeDistribution of Catalysts and Catalyst Carriers by Mercury IntrusionPorosimetry; and Washburn, E. W; The Dynamics of Capillary Flow (1921);Physical Review 1921, 17(3), 273, Mercury porosimetry, such as describedabove, is the preferred method for determining the pore volumes and porediameters of the extruded titania-based materials according to thepresent invention.

The porous, extruded titania-based material according to the presentinvention may be prepared by any suitable extrusion process known tothose skilled in the art, but modified so that one or more acids,preferably an aqueous solution thereof, is mixed with titanium dioxidebefore the extrusion step, and, preferably, so that after extrusion atleast a portion of the one or more acids is removed. Where the porous,extruded titania-based material according to the present inventioncomprises mesopores and macropores, the process is also modified so thatone or more porogens are included in the titania-based material duringextrusion, and are subsequently removed by thermal or oxidativedecomposition.

The porous, extruded titania-based material according to the presentinvention may be prepared using any suitable form of titanium oxide,such as titanium dioxide (CAS No: 13463-67-7), titanium dioxide anatase(CAS No: 1317-70-0), titanium dioxide rutile (CAS No: 1317-80-2),titanium dioxide brookite (CAS No; 98084-96-9), and admixtures orcomposites thereof.

Where the porous, extruded titania-based material according to thepresent invention is to be used as a catalyst support, it is preferablysubstantially free of extraneous metals or elements which mightadversely affect the catalytic activity of the system. Thus, preferredporous, extruded titania-based materials according to the presentinvention are preferably at least 95% w/w pure, more preferably at least99% w/w pure. Impurities preferably amount to less than 1% w/w, morepreferably less than 0.6% w/w and most preferably less than 0.3% w/w.The titanium oxide from which the porous, extruded titania-basedmaterial is formed is preferably of suitable purity to achieve the abovepreferred purity in the finished extruded product.

In the processes for the preparation of a porous, extruded titania-basedmaterial according to the present invention, titanium dioxide and one ormore acids are mixed to form a homogenous paste. Preferably the one ormore acids are mixed with the titanium dioxide as a solution, mostpreferably as an aqueous solution, which may be formed either before themixing takes places (i.e. by dissolving the one or more acids beforemixing with the titanium dioxide) or during the mixing stage (i.e. bymixing titanium dioxide and one or more solid acids and adding asuitable solvent, preferably water). The titanium dioxide and one ormore acids may be mixed using any suitable technique to form ahomogenous mixture, such as by mixing in a mechanical mixer. Ifnecessary, the wetness of the mixture of titanium dioxide and one ormore acids may be adjusted to form an extrudable paste by adding aliquid extrusion medium. Any suitable liquid extrusion medium may beused, i.e. any liquid capable of causing the titanium dioxide and one ormore acids to form a homogenous paste suitable for extrusion. Water isan example of a suitable liquid extrusion medium.

Where the one or more acids is dissolved prior to mixing with titaniumdioxide, it may be dissolved at any suitable concentration, preferablyso that all of the one or more acids is dissolved and/or so that when anamount of the one or more dissolved acids sufficient to provide therequired final amount of acids is mixed with the titanium dioxide themixture will not be too wet to form a homogenous paste suitable forextrusion. Suitably, the one or more acids may be used at aconcentration of 0.1 mol/litre or above, preferably 0.5 mol/litre orabove.

The porous, extruded titania-based material comprising mesopores andmacropores according to the present invention may be prepared using anysuitable porogen, i.e. a material capable of enabling the formation ofmacropores in an extruded titania-based material once it has beenremoved therefrom, for example by thermal or oxidative decomposition.

Suitable porogens for use in the processes for the production of aporous, extruded titania-based material comprising mesopores andmacropores according to the present invention comprise cellulose orderivatives thereof, such as methyl cellulose (CAS No: 9004-67-5), ethylcellulose (CAS No: 9004-57-3) and ethyl methyl cellulose (CAS No:9004-69-7); alginic acid (CAS No: 9005-32-7) or derivatives thereof,such as ammonium alginate (CAS No: 9005-34-9), sodium alginate (CAS No:9005-38-3) and calcium alginate (CAS No: 9005-35-0); latex, such aspolystyrene latex (CAS No: 26628-22-8) or polyvinylchloride (CAS No:9002-86-2).

The proportion of total porogen to titanium dioxide used in theprocesses of the present invention may be selected so as to provide asuitable proportion of macropores in the porous, extruded titania-basedmaterial. However, a preferred weight ratio of titanium dioxide to totalporogen is from 1:0.1 to 1:1.0, preferably 1:0.1 to 1:0.8, morepreferably 1:0.15 to 1:0.6.

Where a process of the present invention includes mixing one or moreporogens with titanium dioxide to form a homogenous mixture, the porogenmay be mixed with titanium dioxide either before or after mixing withthe one or more acids, or at the same time as the addition of the one ormore acids. Preferably, the titanium dioxide and one or more porogensare mixed to form a homogenous mixture before the addition of the one ormore acids to the homogenous mixture. Mixing of the titanium dioxide andone or more porogens may be carried out in the same apparatus as themixing with one or more acids or in different equipment, as required,

A process for the production of a porous, extruded titania-basedmaterial, according to the present invention may optionally furthercomprise a mulling step to reduce the presence of larger particles thatmay not be readily extruded, or the presence of which would otherwisecompromise the physical properties of the resulting extrudate. Anysuitable mulling or kneading apparatus of which a skilled person isaware may be used for mulling in the context of the present invention.For example, a pestle and mortar may be suitably used in someapplications or a Simpson Muller may suitably be employed. Mulling istypically undertaken for a period of from 3 to 90 minutes, preferablyfor a period of 5 minutes to 30 minutes. Mulling may suitably beundertaken over a range of temperatures, including ambient temperatures.A preferred temperature range for mulling is front 15° C. to 50° C.Mulling may suitably be undertaken at ambient pressures.

The homogenous paste formed in a process for the production of a porous,extruded titania-based material according to the present invention maybe extruded to form an extrudate using any suitable extruding methodsand apparatus of which the skilled person is aware. For example, thehomogenous paste may be extruded in a mechanical extruder (such as aVinci VTE 1) through a die with an array of suitable diameter orifices,such as 1/16 inch diameter, to obtain extrudates with cylindricalgeometry.

The extrudate formed in a process for the production of a porous,extruded titania-based material according to the present invention maybe dried and/or calcined at any suitable temperature. Where the processincludes the incorporation of a porogen before the extrusion step, thedrying and/or calcining is preferably carried out at temperaturessufficient to decompose the one or more porogens.

Where the process of the present invention includes both drying andcalcining, the drying step is preferably carried out before thecalcining step.

Drying in accordance with the present invention is suitably conducted attemperatures of front 50° C. to 150° C., preferably 75° C. to 125° C.Suitable drying times are from 5 minutes to 24 hours. Drying maysuitably be conducted in a drying oven or in a box furnace, for example,under the flow of an inert gas at elevated temperatures.

Preferably, a calcining step is incorporated in the processes of thepresent invention, to ensure that at least a portion, preferably asignificant portion, more preferably substantially all, of the one ormore acids is removed from the finished extrudates.

Calcination may be performed by any method known to those of skill inthe art, for example in a fluidized bed or a rotary kiln, suitably at atemperature of at least 400° C., such as at least 420° C., morepreferably at least 500° C., and yet more preferably at 500-700° C.

The Fischer-Tropsch synthesis catalyst according to the presentinvention comprises a porous, extruded titania-based material,preferably comprising mesopores and macropores, according to the presentinvention, or obtainable by a process according to the presentinvention, and further comprises at least one metal selected fromcobalt, iron, nickel, ruthenium or rhodium, preferably cobalt. Theamount of metal, on an elemental basis, present in the Fischer-Tropschsynthesis catalyst according to the present invention is suitably from5.0 wt % to 30.0 wt %, preferably 7.0 wt % to 25.0 wt %, more preferably10 wt % to 20 wt %, based on foe total weight of the catalyst. As willbe appreciated by the skilled person, the amount of metal, on anelemental basis, present in the Fischer-Tropsch synthesis catalyst maybe readily determined by X-ray fluorescence (XRF) techniques.

The Fischer-Tropsch synthesis catalyst according to the presentinvention is preferably produced using one or more acids selected fromorganic acids (carboxylic acids) or inorganic acids (mineral acids) thatmay be removed and/or decomposed from the catalyst, such as propionicacid, malic acid, oxalic acid, valeric acid, carbonic acid, formic acid,citric acid, acetic acid, nitric acid and mixtures thereof, preferablyacetic acid, formic acid, citric acid, nitric acid and mixtures thereof,more preferably nitric acid, acetic acid and mixtures thereof.

Preferably the Fischer-Tropsch synthesis catalyst according to thepresent invention is substantially or entirely free of acids.

The Fischer-Tropsch synthesis catalyst according to the presentinvention may additionally comprise one or more promoters, dispersionaids, binders or strengthening agents. Promoters axe typically added topromote reduction of an oxide of metal to pure metal; for example cobaltto cobalt metal, preferably at lower temperatures. Preferably, the oneor more promoters are selected from rhenium, ruthenium, platinum,palladium, molybdenum, tungsten, boron, zirconium, gallium, thorium,manganese, lanthanum, cerium or mixtures thereof. The promoter istypically used in a metal to promoter atomic ratio of up to 250:1, andmore preferably up to 125:1, still more preferably up to 25:1, and mostpreferably 10:1.

The Fischer-Tropsch synthesis catalyst according to the presentinvention may be prepared by incorporating a solution of at least onethermally decomposable cobalt, iron, nickel, ruthenium or rhodiumcompound into a process for the production of a porous, extrudedtitania-based material according to the present invention, i.e. byadding the solution of at least one thermally decomposable cobalt, iron,nickel, ruthenium or rhodium compound at any stage before extrusion ofthe homogenous paste. Preferably, the solution of at least one thermallydecomposable cobalt, iron, nickel, ruthenium or rhodium compound isadded following mixing of the titanium oxide and one or more acids.

Alternatively, a Fischer-Tropsch synthesis catalyst according to thepresent invention may be prepared by impregnating a porous, extrudedtitania-based material, preferably comprising mesopores and macropores,according to the present invention with a solution of at least onethermally decomposable cobalt, iron, nickel, ruthenium or rhodiumcompound. Impregnation of the porous, extruded titania-based materialwith the solution of at least one thermally decomposable cobalt, iron,nickel, ruthenium or rhodium compound in accordance with the presentinvention may be achieved by any suitable method of which the skilledperson is aware, for instance by vacuum impregnation, incipient wetnessor immersion in excess liquid. The impregnating solution may suitably beeither an aqueous solution or a non-aqueous, organic solution of thethermally decomposable metal compound. Suitable non-aqueous organicsolvents include, for example, alcohols, ketones, liquid paraffinichydrocarbons and ethers. Alternatively, aqueous organic solutions, forexample an aqueous alcoholic solution, of the thermally decomposablemetal-containing compound may be employed. Preferably, the solution ofthe thermally decomposable metal-containing compound is an aqueoussolution.

Suitable metal-containing compounds are those which are thermallydecomposable to an oxide of the metal following calcination, or whichmay be reduced directly to the metal form following drying and/orcalcination, and which are completely soluble in the impregnatingsolution. Preferred metal-containing compounds are the nitrate, acetateor acetyl acetonate salts of cobalt, iron, nickel, ruthenium or rhodium,most preferably the nitrate, for example cobalt nitrate hexahydrate.

Following extrusion, the extrudate may be dried and/or calcined at atemperature sufficient to convert the at least one thermallydecomposable cobalt, iron, nickel, ruthenium or rhodium compound to anoxide thereof or to the metal form.

Following impregnation, the impregnated extrudate may be dried and/orcalcined at a temperature sufficient to convert the at least onethermally decomposable cobalt, iron, nickel, ruthenium or rhodiumcontaining compound to an oxide thereof or to the metal form.

The drying and calcining temperatures and conditions suitable forproducing a porous, extruded titania-based material according to thepresent invention are also suitable for use in the processes forpreparing Fischer-Tropsch synthesis catalysts according to the presentinvention.

Where an oxide of cobalt, iron, nickel, ruthenium or rhodium is formedduring a process for die preparation of a Fischer-Tropsch synthesiscatalyst according to the present invention, the material may be used asa catalyst in a Fischer-Tropsch reaction without further processing, andthe oxide of cobalt, iron, nickel, ruthenium or rhodium will beconverted to the metal form during such use. Alternatively, the materialcomprising an oxide of cobalt, iron, nickel, ruthenium or rhodium mayoptionally be heated under reducing conditions to convert the at leastone cobalt, iron, nickel, ruthenium or rhodium oxide to the metal formbefore use as a Fischer-Tropsch synthesis catalyst. Any suitable meansfor converting the oxide of cobalt, iron, nickel, ruthenium or rhodiumto the metal form known to those skilled in the art may be used.

Where promoters, dispersion aids, binders and/or strengthening aids areincorporated in the Fischer-Tropsch synthesis catalyst according to thepresent invention, the addition of these materials may be integrated atseveral stages of the process according to the present invention.Preferably, the promoter, dispersion aids, binder or strengthening aidsare admixed during any stage prior to extrusion, or during theimpregnation step.

The Fischer-Tropsch synthesis catalyst comprising a porous, extrudedtitania-based material according to the present invention or aFischer-Tropsch synthesis catalyst obtainable by a process according tothe present invention will preferably have a crush strength of greaterthan 5.0 lbf, more preferably greater than 7.0 lbf, and even morepreferably greater than 10.0 lbf. The upper limit of the crush strengthof the Fischer-Tropsch synthesis catalyst according to the presentinvention is not particularly critical, but a suitable upper crushstrength is 25.0 lbf. Particularly preferred ranges of crush strengthfor Fischer-Tropsch synthesis catalysts according to the presentinvention are 5.0 lbf to 25.0 lbf, preferably 7.0 lbf to 20.0 lbf, morepreferably 10.0 lbf to 17.0 lbf.

The Fischer-Tropsch synthesis catalyst comprising a porous, extrudedtitania-based material according to tire present invention or aFischer-Tropsch synthesis catalyst obtainable by a process according tothe present invention may be used as a catalyst in any conventionalFischer-Tropsch process for converting a mixture of hydrogen and carbonmonoxide gases to hydrocarbons. The Fischer-Tropsch synthesis ofhydrocarbons from a mixture of hydrogen and carbon monoxide, such assyngas, may be represented by Equation 1:

mCO+(2m+1)H₂ →mH₂O+C_(m)H_(2m+2)  Equation 1

As discussed hereinbefore, the Fischer-Tropsch synthesis catalystsaccording to the present invention or obtainable by the process of thepresent invention have improved crush strength and are therefore bettersuited for use in fixed-bed Fischer-Tropsch processes. Additionally,Fischer-Tropsch synthesis catalysis according to the present invention,or obtainable by a process of the present invention, and comprisingmesopores and macropores have been surprisingly found to have improvedcatalyst activity and/or selectivity, particularly reduced selectivityfor methane. The Fischer-Tropsch synthesis catalyst according to thepresent invention, or obtainable by a process according to the presentinvention, therefore provides particularly useful ranges of hydrocarbonswhen used in a Fischer-Tropsch reaction.

A composition according to the present invention comprising hydrocarbonsobtained by a process of the present invention is preferably a fuelcomposition, for example a gasoline, diesel or aviation fuel orprecursor thereof.

The present invention will now be illustrated by way of the followingExamples.

EXAMPLES Comparative Example 1 Titania Extrudate Formed with DistilledWater

Titanium dioxide (BASF P25) was mixed in a mechanical mixer (Vinci MX0.4) with sufficient distilled water to form an extrudable paste, forexample at a water to titanium mass ratio of 0.66 g/g. The resultantpaste was extruded through a die with an array of 1/16 inch circularorifices using a mechanical extruder (Vinci VTE1) to obtain extrudateswith cylindrical shape.

The extrudates were air dried for one hour, then dried at a temperatureof between 100 and 120° C. overnight, followed by calcination in airflow at 500° C. for four hours, via a ramp of 2° C./min.

The mechanical strength of the extrudates was analysed using a VarianBenchsaver™ V200 Tablet Hardness Tester. 50 particles were analysed ineach test, and the mean value was calculated.

The surface area of the extrudates was estimated using the BET model tothe nitrogen adsorption branch of the isotherms collected at 77K on aQuadrasorb SI unit (Quantachrome).

The physical properties of the extrudates were as follows:

Geometry: 1/16 inch diameter cylinder

Crush strength: 4.7 lbf

BET surface area: 51 m²/g

Example 1 Titania Extrudate Prepared Using 1.0 Mol/L Nitric Acid

The procedure of Comparative Example 1 was repeated, with the exceptionthat the distilled water was replaced by a 1.0 mol/L aqueous solution ofnitric acid.

The physical properties of the extrudates of Example 1 were determinedas set out in Comparative Example 1, and the results are as follows:

Geometry: 1/16 inch diameter cylinder

Crash strength: 13.7 lbf

BET surface area: 42 m²/g

Compared with the pure titania extrudates prepared in ComparativeExample 1, the extrudates of Example 1 prepared using 1.0 mol/L nitricacid exhibited substantially higher mechanical strength.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope and spirit of this invention.

1. A porous, extruded titania-based material further comprising one ormore acids.
 2. A porous, extruded titania-based material according toclaim 1, in the form of symmetrical cylinders, dilobes, trilobes,quadralobes or hollow cylinders.
 3. A porous, extruded titania-basedmaterial according to claim 1, having a crush strength of greater than3.0 lbf.
 4. A porous, extruded titania-based material according to claim1, wherein the one or more acids comprises propionic acid, malic acid,oxalic acid, valeric acid, carbonic acid, formic acid, citric acid,acetic acid, nitric acid, hydrochloric acid, hydrofluoric acid,hydrobromic acid, hydroiodic acid, phosphoric acid, sulphuric acid andmixtures thereof.
 5. A porous, extruded titania-based material accordingto claim 1, comprising mesopores and macropores.
 6. A porous, extrudedtitania-based material according to claim 5, wherein the mesopores havea pore diameter of 2 to 50 nm.
 7. A porous, extruded titania-basedmaterial according to claim 5, wherein the macropores have a porediameter of greater than 50 nm.
 8. A porous, extruded titania-basedmaterial according to claim 5, wherein the total pore volume is at least0.30 ml/g.
 9. A porous, extruded titania-based material according toclaim 5, wherein the surface area is at least 30 m²/g.
 10. A process forthe preparation of a porous, extruded titania-based material having acrush strength greater than 3.0 lbf, said process comprising: a) mixingtitanium dioxide and one or more acids, and optionally a liquidextrusion medium, to form a homogenous paste; b) extruding the paste toform an extrudate; and c) drying and/or calcining the extrudate.
 11. Aprocess according to claim 10 wherein the one or more acids comprisespropionic acid, malic acid, oxalic acid, valeric acid, carbonic acid,formic acid, citric acid, acetic acid, nitric acid, hydrochloric acid,hydrofluoric acid, hydrobromic acid, hydroiodic acid, phosphoric acid,sulphuric acid and mixtures thereof.
 12. A porous, extrudedtitania-based material obtainable by the process of claim
 10. 13. Aprocess for the preparation of a porous, extruded titania-based materialcomprising mesopores and macropores and having a crush strength greaterthan 3.0 lbf, said process comprising: a) mixing titanium dioxide andone or more porogens to form a homogenous mixture; b) adding of one ormore acids, and optionally a liquid extrusion medium, to the homogenousmixture, and mixing to form a homogenous paste; c) extruding the pasteto form an extrudate; and d) drying and/or calcining the extrudate at atemperature sufficient to decompose the one or more porogens.
 14. Aprocess according to claim 13, wherein the one or more acids comprisespropionic acid, malic acid, oxalic acid, valeric acid, carbonic acid,formic acid, citric acid, acetic acid, nitric acid, hydrochloric acid,hydrofluoric acid, hydrobromic acid, hydroiodic acid, phosphoric acid,sulphuric acid and mixtures thereof.
 15. A process according to claim13, wherein the one or more porogen comprises cellulose or a derivativethereof, such as methyl cellulose, ethyl cellulose and ethyl methylcellulose; alginic acid or a derivative thereof, such as ammoniumalginate, sodium alginate and calcium alginate; latex or polyvinylchloride.
 16. A process according to claim 13, wherein the weight ratioof titanium dioxide to porogen is from 1:0.1 to 1:1.0.
 17. A porous,extruded titania-based material obtainable by a process according toclaim
 13. 18-32. (canceled)
 33. A porous, extruded titania-basedmaterial according to claim 5, wherein the mesopores have a porediameter of 25 to 40 nm.
 34. A porous, extruded titania-based materialaccording to claim 5, wherein the macropores have a pore diameter of 100to 850 nm.
 35. A porous, extruded titania-based material according toclaim 5, wherein the total pore volume is at least 0.30 ml/g, and thesurface area is at least 30 m²/g.